DESCRIPTION: (Applicant's Abstract) The first purpose of this project is to understand the molecular mechanisms responsible for the constitutive activation of the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signal transduction pathways in some cases of acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and chronic myelogenous leukemia (CML). The second purpose of this project is to determine the importance of constitutive JAK2/STAT5 activation in development and maintenance of the leukemic phenotype, both in vitro and in vivo. The primary hypotheses being tested are that specific activating mutations that lead to constitutive activation of JAK/STAT signal transduction pathways are responsible for the development and/or maintenance of leukemic cell survival and proliferation, and that, in leukemic cells expressing constitutively activated STAT5, inhibition of STAT5 activation or function. Three specific aims are proposed to test these hypotheses. Specific Aim 1 is to determine the mechanism(s) of constitutive activation in the HEL/Dami and Meg-01 human leukemic cell lines. Specific Aim 2 is to determine whether constitutive JAK/STAT signaling pathway activation plays an important role in maintenance of the leukemic phenotype of primary human AML cells. Specific Aim 3 is to determine the ability of double-stranded "decoy" oligonucleotides containing the STAT5 binding domain to inhibit the unregulated survival and proliferation of leukemic cells in vivo. The models to be tested include: (1) human HEL/Dami and Meg-01 cell lines implanted in sublethally irradiated NOD/SCID mice; (2) tet-off bcr/abl transgenic mice, which develop leukemia when mice are deprived of tetracycline in their drinking water (obtained from Dan Tenen); and (3) mice transplanted with bone marrow cells transfected with TEL/JAK2 or TEL/ABL retroviruses, which result in development of leukemias that have constitutively activated STAT5. These studies should lead to new understanding approaches for treatment of leukemias in which STAT activation plays a role in maintenance of the leukemic phenotype.